Pipetting means and method of operating a pipetting means

ABSTRACT

A pipetting means includes a micropump comprising a pump chamber with a first opening and a second opening. Furthermore, the micropump includes means for changing the volume of the pump chamber. A first active valve is provided to perform opening and closing the first opening. Furthermore, a second active valve is used to perform opening and closing the second opening. Furthermore, the pipetting means comprises a pipette tip connected to the first or second opening via a pipette channel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending International Application No. PCT/EP 03/06389, filed Jun. 17, 2003, which designated the United States and was not published in English and is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to pipetting means and more specifically to pipetting means with micropumps.

2. Description of the Related Art

With increasing enhancement of the manufacture of micromechanical structures, today various devices may be realized as microstructure devices. Such a microstructure device, for example, includes a micropipetting means with a micropump.

FIG. 1 shows a known pipetting means having first and second micropumps 110 a and 110 b each constructed of three pump body sections 110, 112 and 114 arranged on top of each other. The pump body sections 110, 112 and 114 each include a flat disc or wafer with microstructures created by means of suitable etching methods. Typically, the pump body sections 110, 112 and 114 in such a known micropump comprise semiconductor material, such as silicon. Each of the micropumps 110 a and 110 b includes a pump chamber 116 formed by boundaries of the pump body sections 110-114. The pump chamber 116 comprises an inlet opening 118 formed in the lower pump body section 110. Above the inlet opening 118, a first flapper valve formed as passive check valve is arranged. The flapper valve 120 is formed in the center pump body section 112 and comprises an elongated flexible flapper 120 a extending across the inlet opening 118.

The pump chamber 116 further comprises an outlet opening 122, which can be closed and opened by a second passive flapper valve 124 arranged in the pump body section 110. The second flapper valve 124 comprises a flapper 124 a with a longitudinal flexible shape, corresponding to the first flapper valve 120.

Furthermore, the micropumps 100 a and 100 b comprise a piezoelectric actuation element 126 for changing the volume of the pump chamber. The piezoelectric actuation element 126 is arranged as a piezoelectric ceramics layer in large area manner on a thinly formed membrane 128 flexibly arranged between holding elements. On applying a suitable voltage to the piezoelectric actuation element 126, the membrane 128 deforms and causes, depending on the polarity of voltage, enlarging or reducing the volume of the pump chamber 116.

In a suction process, a voltage deforming the membrane 128 such that an enlargement of the volume of the pump chamber 116 results is applied to the piezoelectric actuation element 126. Here, in the pump chamber 116, negative pressure is generated, which causes the valve 120 to transition from a closed state to an open state, whereas the valve 124 comprises a closed state by the negative pressure. Thereby, fluid is sucked through the opening 118 into the pump chamber 116.

In a pumping process, the pump chamber volume is decreased by applying an electric voltage to the piezoelectric actuation element 116. The positive pressure developing here causes a force moving the flapper valve 124 downward to be applied to the flapper valve 124. Thereby, the opening 122 is opened, whereas the inlet opening 118 is closed by the valve 120. By the positive pressure in the pump chamber 116, the fluid is expelled from the pump chamber 116 through the opening 122.

The micropumps 100 a and 100 b are arranged in the pipetting means such that the micropump 100 a is connected to a pipette channel 132 of a pipette tip 134 on the suction side, i.e. with the inlet opening 118, and to an environment on the pressure side, i.e. with the outlet opening 122. But the micropump 100 b is connected in opposite direction relative to the micropump so that it is connected to the pipette channel on the pressure side and to the environment on the suction side.

When sucking a medium to be dosed, the micropump 100 a attached to the pipette channel on the suction side is actuated so that the volume of the pump chamber increases and air from the pipette channel is sucked into the pump chamber. Here, an air cushion 136 in the pipette tip 134 is reduced and a dosing medium 138 is sucked into the pipette tip 134. The second micropump 100 b in connection to the pipette channel on the pressure side remains switched off here.

Conversely, when dosing the sucked medium, the micropump 100 b is actuated by decreasing the volume of the pump chamber thereof, whereas the micropump 100 a remains switched off. The micropump 100 b connected to the pipette channel on the pressure side here generates a positive pressure in the pipette channel causing build-up of the aircushion 136 and expulsion of the dosing medium.

The above-described micropumps 100 a and 100 b distinguish themselves by simple control, since in the pumping and suction processes only the piezoelectric actuation element 126 has to be actuated as single active element. Furthermore, an advantage of the micropumps 100 a and 100 b is that they can be manufactured in compact manner in that, on a chip on which the micropumps are arranged, only little area is consumed. Moreover, there is long-year experience for such known micropumps with flapper valves, so that the structures of the micropump can be created with high accuracy.

The use of passive check valves in the micropumps 100 a and 100 b, which open or close with positive and negative pressures, respectively, however have the disadvantage that holding the liquid is not always guaranteed. Already small positive pressure at the inlet opening 118 may cause the passive check valve to open slightly, whereby fluid may flow into the pump chamber or flow out.

In the employment of the micropumps 100 a and 100 b in the above-described pipetting means, due to the above-described insufficient holding of the dosing liquids, therefore leaking rates already occur with small pressure differences in opening direction. Particularly holding large amounts of liquids is only possible in limited manner due to the hydrostatic pressure and the leaking rates connected thereto.

A substantial disadvantage of the micropumps 100 a and 100 b further consists in that, at high pressure pulses, a so-called fluidic short may occur. If the micropump 100 a is actuated during sucking the dosing fluid, a pressure p2 smaller than a pressure p1 of the environment in connection with the outlet opening of the micropump 100 a develops in the pipette channel 132. Since, however, the pipette channel is in connection with the outlet opening of the micropump 100 d and also the environment with the inlet opening of the micropump 100 b, the pressure difference causes the valves of the micropump 100 b to maybe open due to the pressure difference, so that a fluidic short occurs through the micropump 100 b. Furthermore, a fluidic short may also occur in expelling the dosing fluid. In this case a pressure p2 greater than the pressure p1 of the environment in connection with the inlet opening of the micropump 100 b is generated in the pipette channel by actuating the micropump 100 b. By the pressure difference between the environment and the pipette channel, the valves of the micropump 100 a may open, so that a fluidic short through the micropump 100 a may occur in a dosing process.

As it is known, the danger of the fluidic short may be reduced by suitably controlling the piezoelectric element 126, in which short-term high pressure pulses are avoided. Controlling the piezoelectric element 126 may for example take place by means of a sinusoidal waveform. Generating the sine form, however, requires incremental circuitry by having to provide additional devices and circuit components.

A further disadvantage of the above-described known pipetting means is that the manufacture thereof is expensive. The micropumps 100 a and 100 b are formed of three wafers arranged on top of each other after structuring. Arranging the wafers requires high precision so that the structures of the various wafers each arranged on top of each other are accurately positioned at the intended position. Here, the effort increases with each additional wafer.

Furthermore, with the known micropumps 100 a and 100 b, the center pump body section 112 has to be formed thinly, in order to keep an overall height of the pump chamber 116 small, so that high compression capability is achieved. Thinning the wafer is performed by means of grinding, as it is known. By the grinding, however, mechanical stresses occur, which may lead to damage of the sensitive microstructures or the breaking of the wafer.

Alternatively, in the manufacture of the center pump body section, also a thin wafer may be used as starting wafer. In order to suitably transport and store the thin wafers during the manufacturing process, however, expensive handling devices specially adapted to the thin wafers are required. Furthermore, when handling thin wafers, there is the danger of breakage of the wafer, whereby in mass production the rejection rate is increased and the production costs rise.

A further disadvantage resulting by the use of passive check valves in the micropumps 100 a and 100 b is that simple fluid guidance is not possible, because the fluid stream is impeded in flowing in and out by the flappers. In particular, the opening degree of the flappers depends on the positive or negative pressure in the pump chamber, so that, depending on the present pressure, different courses of the fluid result when letting in or streaming out. This has to be taken into account in a design of the micropump.

Furthermore, for forming the outlet flapper valve 124 an outlet channel 130 in the pump body section 110 has to have a large diameter due to the elongated shape of the valve flap 124 a. Thereby, an outer area of the pump body section 110 reduces, whereby mounting the micropump is made more difficult.

Moreover, a substantial disadvantage of the pipetting means according to FIG. 1 is that two micropumps 100 a and 100 b have to be used to achieve sucking and dosing, because the micropumps 100 a and 100 b can only be operated with one pumping direction. This requires great effort in the manufacture and additional consumption of space.

A pipetting means including two micropumps with passive flapper valves, corresponding to the pipetting means described with reference to FIG. 1, is described for example in DE 198 47 869 A1.

WO 99/10 099 A1 discloses a micro dosing system including a micro membrane pump and an open-jet dosing device or doser. The micro membrane pump is connected to a reservoir by means of an input and further comprises an output connected to an input of the open-jet doser by means of a conduit. At the input and output of the micro membrane pump, passive check valves are provided, so that a liquid can be pumped from the reservoir to the open-jet doser. The open-jet doser further includes a pressure chamber with two openings each forming an input and output of the open-jet doser, respectively. The micro membrane pump and the open-jet doser further include a membrane each, to change the volume of the pressure chamber.

DE 197 06 513 A1 shows a micro dosing device comprising a pressure chamber connected to a media reservoir via an inlet, and further comprising an outlet for expelling fluid. The device includes a membrane with an actor in order to change the volume of the pressure chamber. For preventing a backflow through the channel connected to the media reservoir, a valve is arranged between the pressure chamber and the media reservoir. The valve is operable by means of a piezoelectric drive actuating a moveable membrane for closing.

EP 0 725 267 A2 discloses an electrically controllable micropipette including a microinjection pump. The microinjection pump includes a chamber with a chamber valve controllable by means of an electrically controllable actuator device. In operation, the pumping chamber of the microinjection pump is filled with fluid from a supply and then given off via discharge capillary.

EP 0 568 902 A2 shows a micropump with a pumping chamber comprising an inlet and an outlet each comprising a valve to close them. The pumping chamber further comprises a membrane that can be activated by means of a micro-actuation device. In operation, bending the membrane is performed, whereby the pressure in the pumping chamber is reduced, so that liquid enters the pumping chamber through the inlet when the inlet valve is raised from its seat, while the outlet valve remains in a closed position, and is then expelled via the opened outlet valve.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a pipetting means and a method of operating a pipetting means, which enable secure and stable dosing of a dosing fluid.

In accordance with a first aspect, the present invention provides a pipetting apparatus, having a micropump having a pump chamber with a first opening and a second opening; an actor for changing the volume of the pump chamber; a first active valve for opening and closing the first opening; a second active valve for opening and closing the second opening; and a pipette tip connected to the first or second opening via the pipette channel.

In accordance with a second aspect, the present invention provides a method of operating a pipetting apparatus, having a micropump having a pump chamber with a first opening and a second opening; an actor for changing the volume of the pump chamber; a first active valve for opening and closing the first opening; a second active valve for opening and closing the second opening; and a pipette tip connected to the first or second opening via the pipette channel; the method having the steps of actively closing the first or second opening, whereby an environment is disconnected from the pump chamber; actively opening the second or first opening, whereby the pump chamber is connected to the pipette channel; enlarging the volume of the pump chamber for sucking dosing fluid through the pipette tip; and reducing the volume of the pump chamber for expelling dosing fluid through the pipette tip.

The present invention is based on the finding that a pipetting means with a micropump with stable and secure dosing behavior can be realized by refraining from using a micropump with passive valves for opening or closing openings of a pump chamber. According to the present invention, in the inventive pipetting means, a micropump with active valves is used for opening and closing the pump chamber openings.

Thereby, the openings of the pump chamber can be closed securely even when backpressures occur. This prevents a fluidic short at high pressure pulses and avoids the occurrence of leaking rates.

The inventive use of a micropump with active valves enables operating in two pumping directions, so that only one micropump is required for sucking and dosing.

By providing active valves, also a simple fluid guidance is achieved, because a course of the fluid flowing in or out is not impeded by the flappers, in contrast to the known micropumps with flapper valves. Thereby, also simple fluid guidance results in inlet and outlet channels connected to the openings. Furthermore, the openings may be formed with simple and symmetric shape. This simplifies structuring the openings in the manufacture of the micropump.

Moreover, in the inventive pipetting means, a production process is kept simple, because the critical creating of thin flexible flappers is not required.

In contrast to the known pipetting means with a micropump with passive flapper valves, in the inventive pipetting means it is not required to arrange an elongated valve flap in a largely dimensioned outlet channel of a pump body. Thereby, an outer surface of the pump body may comprise a large mounting area for mounting the micropump to a support, so that simple and secure mounting of the micropump is possible.

A preferred embodiment of the present invention includes a pipetting means with a micropump, in which the active valves include piezoelectric valves. Furthermore, the means for changing the volume of the pump chamber preferably comprises a pump membrane actuatable with a piezoelectric actuation means for changing the volume. The piezoelectric actuation means preferably includes a thin piezo-active layer applied on an outer side of the pump membrane.

The pump membrane is preferably arranged between holding elements enabling bending of the membrane, without having to accept disadvantageous effects on the active valves.

The micropump is preferably formed with a layer structure of two structured flat discs arranged on top of each other. Thereby, the manufacture of the micropump is kept simple and inexpensive. Preferably, semiconductor material, and particularly preferably, silicon material is used as material of the discs.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will become clear from the following description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a cross-sectional illustration of a known pipetting means comprising two micropumps with passive flapper valves;

FIG. 2 is a schematic cross-sectional illustration of an embodiment of a micropump used in a pipetting means according to the present invention; and

FIG. 3 is a schematic cross-sectional illustration of an embodiment of a pipetting means with a micropump according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, with reference to FIG. 2, a micropump 200 is explained, which is employed in one embodiment of the present invention.

According to FIG. 2, the micropump 200 comprises a pump body 210 preferably formed of a disc-shaped first pump body section 212 and a disc-shaped second pump body section 214. The pump body sections 212 and 214 are arranged on top of each other in vertical direction (y axis) and connected to each other at peripheral regions thereof via connection structures. The pump body sections 212 and 214 preferably include discs of a semiconductor material, and particularly preferably of silicon. The pump body 210 may however, in other embodiments, comprise any other micro-structurable material. The disc-shaped pump body sections 212 and 214 are preferably structured by means of known lithography and etching techniques and connected by means of known connection techniques for forming the pump body 210.

A longitudinally formed pump chamber 216 is formed in the micropump 200 by a recess 218 in the lower pump body section 212 and a well-shaped recess 220 in the upper pump body section 214. The recesses 218 and 220 facing in direction of the pump body are preferably arranged in centered manner in horizontal direction (x axis) to achieve a symmetrical structure. Preferably, the pump chamber is formed with small height to achieve a high compression ratio.

The micropump further comprises two openings 222 and 224 letting fluid into the pump chamber 116 or letting it out, which are each formed on opposite sides of the pump chamber 216 in the lower pump body section 212. The openings 222 and 224 each extend in the shape of a truncated cone from a surface facing outward with respect to the pump body 210 to a surface of the lower pump body section 212 facing inward. The openings may, however, also be formed with other shapes, such as a cylinder shape. Preferably, the openings 222 and 224 have a symmetrical shape to simplify manufacture thereof.

Above the opening 222, a first active valve 226 for closing and opening the opening 222 is arranged. The first active valve 226 includes a closing element 228 formed on an inner surface with respect to the pump body 210 of the second pump body section 214. The closing element 228 is formed such that it is spaced in vertical direction from the opening 222 in an opened state of the first active valve 226.

The closing element 228 comprises a flat closing surface extending in horizontal direction across valve seat structures 222 a and 222 b arranged lateral to the opening 222, so that the opening 222 is completely closed by the closing element 228 in a closed state of the valve 226. The valve seat structures 222 a and 222 b are preferably formed such that, when closing the valve 226, the rest area of the closing element 228 is kept small. The small rest area causes secure closing by the closing element 228, because the danger of leaky closing, for example by uneven places in the valve seat structures 222 a and 222 b, is minimized with decreasing rest area.

The closing element 228 is connected to holding elements 232 and 234 each laterally by thin ridges. Thereby, the closing element 228 is arranged flexibly with reference to the holding elements 232 and 234 and can be brought from an opened state to a closed state, in which the closing element 228 rests on the valve seat structures 222 a and 222 b with a closing surface and closes the opening 222.

In order to cause the opening and closing of the first active valve, a first piezoelectric actuation element 230 is arranged on a surface of the closing element 228 opposite the closing surface. The first piezoelectric actuation element 230 preferably includes a thin layer of piezoelectric material, such as quartz.

The first piezoelectric actuation element 230 can be connected to a control means (not shown) via electric terminals (not shown), in order to achieve, by applying an electric voltage, a contraction or expansion of the first piezoelectric actuation element 230, each causing vertical displacements of the closing element 228.

Above the opening 224, also a second active valve 236 is formed, which is preferably formed correspondingly to the first valve 226. More specifically, the second active valve 236 comprises a closing element 238 arranged above the opening 224, which is connected to holding elements 242 and 244 via laterally arranged ridges. The second active valve 236 also includes a second piezoelectric actuation element 240 for enabling the vertical movement of the closing element 238. Furthermore, corresponding to the first valve, valve seat structures 224 a and 224 b are each formed laterally to the opening 222.

As will be explained in greater detail later on, the piezoelectric elements 230 and 240, by applying a corresponding electric voltage, cause opening and closing the openings 222 and 224, respectively, so that the pump chamber 216 for letting in or letting out a pumping medium through the openings 222 and 224, respectively, may be closed or opened.

For changing the volume of the pump chamber, the pump chamber 216 comprises a thin membrane 246 arranged between the holding elements 234 and 244. Thereby, the thin membrane 246 is bendable between the holding elements 234 and 244 in flexible manner, so that by actuating the membrane the volume of the pump chamber 216 can be changed. The massively formed holding elements 234 and 244 prevent movement from transferring to the closing elements 228 and 238 in an actuation of the membrane 246, so that a disadvantageous influence on the active valve by the movement of the membrane 246, which may for example lead to opening a closed valve, is prevented. Furthermore, the holding elements 234 and 244 also serve as mounting means enabling mounting the micropump 200 to a support.

On a side of the membrane 246 facing away from the pump body 210, also a piezoelectric membrane actuation element 250 for activating the membrane 246 is arranged. The piezoelectric membrane actuation element 250, like the piezoelectric actuation elements 230 and 240, preferably comprises a thin layer of piezoelectric material. Furthermore, the piezoelectric membrane actuation element 250 can be connected to a control means via electrical terminals (not shown) to enable applying an electric voltage.

The pump 200 is a pump according to the peristalsis principle, in which the actuation elements 230, 240, and 250 are actuated successively in predetermined orders.

Operating the micropump 200 according to this principle is subsequently explained in greater detail.

In the following, at first a first pumping direction is explained, in which fluid is pumped from the opening 222 to the opening 224.

In a suction process, at first the second valve 236 is actuated to close the opening 224. Actuating the second valve 226 takes place by applying an electric voltage to the second piezoelectric element 240, which causes the closing element 238 to be moved downward in horizontal direction for closing the opening 224. Then the first piezoelectric element 230 is actuated to open the opening 222.

Subsequently, a voltage is applied to the piezoelectric membrane actuation element 250 to cause deformation of the membrane 246, so that the volume of the pump chamber 216 increases. Thereby, negative pressure develops in the pump chamber 216, whereby fluid from the opening 222 is sucked into the pump chamber 216. After terminating the suction process, the first valve 226 is closed.

For pumping out the fluid stored in the enlarged pump chamber 216, the second valve 236 is then actuated by applying an electric voltage to the second piezoelectric actuation element 240 to open the opening 224. After opening, a voltage causing the volume of the pump chamber 216 to reduce is applied to the piezoelectric membrane actuation element 250. This causes the fluid to be pressed out of the pump chamber 216 and through the opening 224.

Preferably, the opening 222 is in connection with a first fluid reservoir in the operation of the micropump 200, whereas the opening 224 is in connection to a second fluid reservoir. This causes fluid to be pumped from the first fluid reservoir into the second fluid reservoir in the above-described pumping process. The first and second fluid reservoirs may for example be ambient air or a container with liquid or gas.

After performing the above-described pumping clock, the pumping process may be repeated once or several times in order to pump a desired amount of fluid from the first reservoir to the second reservoir.

For pumping the micropump 200 with a second pumping direction, in which fluid from the opening 224 is pumped to the opening 222, the active valves 226 and 236 are operated in correspondingly interchanged manner with reference to the above explanations.

More specifically, in the second pumping direction, at first the first valve 226 is closed, the second valve 236 is opened, and then the membrane is actuated for enlarging the pump chamber volume, in a suction process. Thereby, fluid is sucked from the opening 224 into the pump chamber 216. Then the second valve 236 closes the opening 224, whereas the first valve 226 opens the opening 222. Subsequently, the membrane 246 is actuated for reducing the pump chamber volume, whereby the fluid in the pump chamber 216 is expelled through the opening 222.

In the following, with reference to FIG. 3, an embodiment of a pipetting means 252 is explained, in which the micropump 200 explained with reference to FIG. 2 is used for dosing the dosing medium.

According to FIG. 3, the micropump 200 is arranged on a support element 254 in the pipetting means 252, wherein a pipette channel 256 formed in the support element 254 is connected to the opening 224 of the micropump.

The pipetting means 252 further comprises a pipette tip 258 comprising, at a front-side end, an opening for sucking and expelling dosing liquid. At a rear-side end, the pipette tip 258 comprises a connection element 260 formed to connect the pipette channel 256 to the interior of the pipette tip 258. Preferably, the connection element 260 is introduced into the pipette channel 256 in releasable manner to enable exchanging the pipette tip 258.

The support element 254 further includes a channel 262 connected, at a first end thereof, to the opening 222 of the micropump 200. A second end of the channel 262, which is arranged laterally at the support element, is in contact with an environment, which for example comprises air.

The pipetting means 252, as it is shown in FIG. 3, may comprise a filter 264 connected to the channel 262 via a connection element 266 a, between the second end of the channel 262 and the environment connected to the channel.

Typically, the environment includes air as medium, so that the filter is preferably formed as an air filter. The filter 264 may include all known filter types, such as particle filters, chemically selectively absorbing filters or electrostatic filters.

Filtering the air prevents contamination of the dosing medium by particles or chemical impurities of the air. Furthermore, impurities, which may prevent densely closing the openings, are prevented from depositing at the active valves. The filter 264 may further comprise an outer connector element 266 b to enable a connection to a suction line disposed outside the support element 252.

In the following, now an operation of the pipetting means 252 is explained in greater detail.

For sucking a dosing medium preferably including a liquid, the micropump 200 is at first operated with a pumping direction, in which a working medium, which is for example air or another gaseous medium, is sucked through the opening 224 from the pipette channel 256, pumped into the pump chamber 216 and into an environment connected to the channel 262 via the opening 222. This pumping direction corresponds to the second pumping direction explained with reference to FIG. 2, so that an illustration of the associated processes of the micropumps can be taken from the corresponding above explanations.

The pumping process for sucking causes negative pressure to develop inside the pipette tip 258, whereby the dosing medium is sucked inside the pipette tip 258. The pumping process for sucking the dosing medium 268 can be repeated until the desired amount of the dosing medium 268 is sucked into the pipette tip 258. During the suction process, the working medium residing in the pipette tip 258 as a gaseous cushion 270 is increasingly displaced by the dosing medium 268. The gaseous cushion 270 causes the pipette channel not to come into contact with the dosing medium. This prevents the dosing medium from being soiled by dosing medium remains of the previous dosing medium present in the channel in an exchange of the pipette tip 258 for dosing another dosing medium.

After the desired dosing medium amount has been sucked, the valve is actuated for closing to achieve holding the dosing medium in the pipette tip 258.

In an ensuing dosing process, the micropump 200 is operated with the reverse pumping direction, in which the working medium of the micropump 200 is sucked from the environment via the opening 222 and pumped into the pipette channel 256 via the opening 224.

This pumping direction corresponds to the first pumping direction explained with reference to FIG. 2, so that it is referred to the corresponding explanations with regard to an exact description of the pumping processes.

Pumping the working medium from the environment into the pipette channel 256 generates positive pressure in the pipette channel 256 and in the gaseous cushion 270, so that the dosing medium 264 is forced out of the pipette tip 258 by the expanding aircushion. The pumping process may be repeated until a desired dosing medium amount has been brought out of the pipette tip 258.

As already mentioned previously, tight closing independent of occurring counterpressure is achieved by the active valves 226 and 236. This has an advantageous effect in the pipetting means 252, because a fluidic short, as can occur in known micropumps with flapper valves, is prevented. The pipetting means 252 thus achieves high dosing accuracy.

Likewise, unwanted release of the dosing medium when holding it in the pipette tip is prevented by the small leaking rates of the active valves.

Although the active valves of the micropump 200 are formed as piezoelectric valves in the described embodiments, other embodiments of the present invention may include other actively actuatable valve types, such as mechanically actuatable valves, electrostatic valves, or electromagnetic valves.

For actuating the membrane, instead of the described piezoelectric actuation means, any other known actuation means for actuating the membrane may be used, such as an electrostatic actuation means.

Furthermore, in other embodiments, any known means may be used, which enables changing the pump chamber volume. Such means may for example include rotatable elements for compressing and decompressing a fluid in the pump chamber.

Although the pump chamber only comprises two openings in the described embodiment, it may also comprise more than two openings with correspondingly associated active valves in alternative embodiments. This enables selective pumping, in which for example various fluids may be pumped alternatingly into the pump chamber from various reservoirs and then be pumped into predetermined other reservoirs via selectively selected openings. In this embodiment, selective mixing of various fluids may be performed in the pump chamber, wherein a mixing ratio is adjustable by controlling the active valves. The use of the pump chamber as “mixing reactor” achieved thereby further has the advantage of good mixing being achieved by the high pressures in the pump chamber.

Furthermore, the pipetting means with a micropump according to the present invention is not limited to the shown embodiment of an aircushion pipetting means. Other embodiments may for example include a pipetting means according to the direct displacement principle or a micro-titer pipetting means, in each of which the inventive micropump for dosing the dosing medium is used.

While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention. 

1. A pipetting apparatus, comprising: a micropump having a pump chamber with a first opening and a second opening; an actor for changing the volume of the pump chamber; a first active valve for opening and closing the first opening; a second active valve for opening and closing the second opening; and a pipette tip connected to the first or second opening via the pipette channel.
 2. The pipetting apparatus of claim 1, wherein the active valves of the micropump include piezoelectric valves.
 3. The pipetting apparatus of claim 1, wherein the actor for changing the volume of the pump chamber includes a membrane and a piezoelectric actuator for actuating the membrane.
 4. The pipetting apparatus of claim 3, wherein the membrane is arranged between holding elements.
 5. The pipetting apparatus of claim 1, further including a pump body including a first disc-shaped body element and a second disc-shaped body element arranged thereupon.
 6. The pipetting apparatus of claim 1, wherein a pump body comprises a semiconductor material.
 7. The pipetting apparatus of claim 1, wherein the pump chamber further comprises at least one further opening; and wherein the micropump further comprises at least another active valve for opening and closing the at least one further opening.
 8. The pipetting apparatus of claim 1, further comprising a filter for filtering a working medium of the micropump.
 9. A method of operating a pipetting apparatus, comprising: a micropump having a pump chamber with a first opening and a second opening; an actor for changing the volume of the pump chamber; a first active valve for opening and closing the first opening; a second active valve for opening and closing the second opening; and a pipette tip connected to the first or second opening via the pipette channel; the method comprising the steps of: actively closing the first or second opening, whereby an environment is disconnected from the pump chamber; actively opening the second or first opening, whereby the pump chamber is connected to the pipette channel; enlarging the volume of the pump chamber for sucking dosing fluid through the pipette tip; and reducing the volume of the pump chamber for expelling dosing fluid through the pipette tip.
 10. The pipetting apparatus of claim 9, wherein the pipetting apparatus is used as an air cushion pipetting apparatus.
 11. The pipetting apparatus of claim 9, wherein the pipetting apparatus is used as a direct displacement pipetting apparatus.
 12. The pipetting apparatus of claim 9, wherein the pipetting apparatus is used as a micro-titer pipetting apparatus. 